Seal for centrifugal machines



April 1950 F. FLETCHER, JR 2,505,391

SEAL FOR CENTRIFUGAL MMMMM NES April 25, 1950 Filed June 23, 1947 F. H. FLETCHER, JR

SEAL FOR CENTRIFUGAL MACHINES 2 Sheets-Sheet 2 INVENTOR.

Frank H. FIE-T131121? Jr.

14 Bw'QZZ w ATTORNEYS.

Patented Apr. 25, 1950 UNITED STATES PATENT OFFICE SEAL FOR CENTRIFUGAL MACHINES Frank H. Fletcher, 31:, Flushing, N. Y.

Application June 23, 1947, Serial No. 756,430

This invention relates to sealing devices, and more particularly to a sealing device applicable to centrifugal machines, centrifugal pumps, turblues and the like, of which the opposite sides of a casing wall through which the shaft extends are exposed to different pressures.

The invention more specifically relates to a 2 Claims. (Cl. 2869) liquid centrifugal seal in which the liquid is rendered effective by centrifugal force to serve as a packing medium for the rotatable shaft, and in which the liquid is mercury.

A seal of this general type employing water, oil,

or similar liquids is described in my application Serial No. 756,429 cocurrently filed herewith, for

a Liquid seal.

The present invention, generally stated, com

rows of line 3-3 of Figure 1,

Figure 4 is a fragmentary side elevation of the seal members and shaft, showing the position of the mercury when the shaft and seal impeller is at rest,

Figure 5 is a fragmentary side elevation of the seal and shaft, showing the position of the merprises a device wherein the sealing is accomj plished by a rotating seal disc packing for forcing the sealing liquid with a centrifugal force outward against the inner circumferential wall of a sealing chamber.

This seal has but one mechanical moving part, other than the sealing liquid, this part being the seal disc. This disc together with the sealing j liquid provides an absolutely air tight seal subject to practically no wear, and no undue friction losses and constant replacement as are seals of the packing or stuffing-box type in which the packing material quickly wears causing the seal to leak and require shut-down of operation for replacement. Due to the minimum of friction, practically no wear, and automatic operation of this seal requiring no replacement of sealing liquid ove long periods of time, it is dependable, efficient in operation and overcomes the objections to the packing or stuffing-box types.

The principal object of this invention is to provide an effective seal where considerable forces are involved between pressure or vacuum chambers containing rotatable elements and the exterior.

An object is to provide a simple and eficient mercury seal that will maintain an effective seal against either a vacuum or a pressure of high order.

A further object is-to provide a mercury seal in which the sealing chamber and seal disc is constricted at the vital portions to permit satisfactory operation with a minimum of mercury and therefore low frictional lossses.

A further object is to provide a mercury seal which is automatic in operation and has ample space for storage of the excess mercury when not in operation.

A further object is to provide a seal disc of improved design or construction most effective for use with mercury as the sealing liquid.

Still further objects and advantages will be apparent from the following description, the claims, and the accompanying drawings in which:

cury when the shaft is rotating and fluid pressure is exerted from the left, and

Figure 6 is a fragmentary side elevation, shW-' ing the position of the mercury when fluid pressure comes from the right.

As shown in Figure 1 the seal housing may consist of circular plates or walls In and II in which the circular seal chamber [2 is formed, bolted by means of cap screws l3 to a pump casing or housing M. A cap l secured to plate I l by means of cap screws [6 is provided with a recess ll for the throw ring l8, while a recess IS in the pump casing I4 is provided for the other throw ring 20.

A pump shaft 2|, turned with stepped portions, is suitably driven by means of any prime mover connected to drive shaft 22 through coupling 23, and the pump impeller or other device to be driven is secured to the pump shaft portion Zia. In th event the seal is to be applied to a steam turbine, for example, the shaft portion 2| a will be the driving end and power will be transmitted via shaft 2|, coupling 23 and shaft 22.

Secured to pump shaft 2|, by means of a key 24 (Figure 3), is a seal impeller 25 having a disc or web portion 26 of slightly smaller diameter than that of the seal chamber l2, in which it rotates, and a plurality of perpendicular vanes 2! whose outer ends form a circle of slightly smaller diameter than that of the web 26.

Th width of the vanes 21 is the same as the length of the seal impeller hub at their hub connected or inner ends and tapered toward their outer or free ends to closely fit the similarly shaped seal chamber l2 and thus provide a relatively large space adjacent the impeller hub for the mercury 28, constituting the sealing liquid shown in Figure 4, when the seal impeller is at rest and all of the mercury therefore in the lower part of the seal chamber and the reservoirs 29 and 30.

When the seal impeller is rotating the mercury 28 is thrown, by means of the impeller vanes 21 to the restricted outmost diametrical inner wall of the seal chamber. The narrowness of the portion of the seal chamber requires a minimum of mercury to seal the space between the outer diametrical portion ofthe seal impeller web portion 26and the'iwalls ofthe seal chamber, the inner level of the mercury under these conditions being but slightly below the outer extremities of the vanes 21 in order that friction losses may be kept to a minimum while assuring an ample depth of mercury to permit the vanes 21.

to continually force the mercury against the outer confines of the seal chamber and thus maintain an effective shaft seal.

Shaft 2| is diametrically stepped in order that the various parts of the sealwhich it supports maybe readily assembled from one end and secured in proper operating position and accessable for. inspection or replacement. Throw rings. 18 and 230i suitable materialiare provided' to prevent any excess mercury from creeping along the shaft. Such mercury as maygreach' the throw rings is returned to the mainreservoirs 29 and Bil.

The main mercury reservoirs '29and til (Figure 5) together with the lowerhalf of the restricted andflared portions of the seal: chamber !2 contains'thefentirefamount of. mercury'when the shaft 2'! is. inoperative and the; mercury level when at'rest should'be' but slightly below the lowest part of. the. shaft opening in the wall of the pump casing 14:; in orderito prevent any possible. loss of mercury; along. the stationary shaft. The size of 'the reservoirs 29 and 39,, together with the size of the lower portion of "the seal chamber'andthe seaLimpel'l'er; should be such as will" accommodat'e'only sumcient'mercury when the seal impeller is at restas willbe require'dfor eificient operation when the impeller is rotating at mercury throwing speeds;

A bore or channel 3l provided with a: closing cap screw '32 is arrangedin plate I l to permit therequired amount ofmercury to be placediand maintained in the seal chamber and mercury reservoirs It will be readily seen that that seal of this invention may be, constructed as a' unit and readily mounted and assembled oirthe outside wa llof a machine whcseshaft is to be sealed and that the seal may be readily opened for inspec tion; repairs or replacements; if necessary.

In. Figure 5'the' level of" the mercury 28a. is indicated with theimpeller rotating athigh speed in 'which case the reservoirs '29-" and '3 are drained or empty'and'the' mercury all confined to the narrowportion of the seal chamber. In this view "the level of -the"mercu ry 2f8a on' either side of the impeller i-ndicat'es the existence of vacuum or suction from the pump impeller chamber into which the shaft end'zia extends.

' In Figure 6, with'conditions otherwise the same as in Figure 5, the level of the mercury 28'sindicates a pressure coming from a pump or turbine chanibeninto which theshaft end 21w extends.

It will be readily understood that whereas water or other suitableliquid could be used in the seal chamber, the use of mercury is necessary where heavy pressures are to be sealed against escape either into. or from within. the pump chamber, It will also be understood that thevanes on the seal impeller are necessary to force the relatively heavy mercury to the area 7 adjacentthe periphery of the sealimpeller web 4 and to maintain it there with sufiicient centrifugal force as will overcome heavy fluid pressures seeking escape along the drive shaft.

In the construction illustrated there is practically n loss; of mercury randfthe entire operation of the seal, after receiving a proper supply of mercury, is automatic with minimum frictional losses and requiring a minimum of attention afterbeing set up.

. V Eorpurposesof definition it will be understood that wherever the noun fluid is used herein itrefers to the dictionary definition of a gas or liquid.

While the preferred embodiment of this invention has beenshown for purposes of illustration, itis to-b'eclearly understood-that various changes in details of" construction andl arrangement of parts may be made without departing; from the scope of the invention as set'forth in the appended-claims. IN '7 Q 7' I I What is claimedisz 1. The combination, in a machine having a wall; a rotatable shaft extending horizontally through said'walL a shaft seal comprising means on said wall forming" a chamber-adapted: to can tain rnercury and surrounding said shaft to be sealed; a vertically disposed impeller in said chamber mounted- 'on and rotatable with said shaft and-adapted to -develop due to centrifugal force in said mercury a sealing force between said impeller and wall or said chamber, and means for automatically storing the excess mer. cury when saidseal impeller is 'stationary, comprising 'the surface of an axially extending reservoir formed.- directly in the wall of said chamber with the upper limit of said reservoir ending at the lowermost surface area efsaid shaft.

2. In a housing foraliquid-sealywalls defining a combined 'horizontal shaft portion and-impeller accommodating and liquid seal chamber and having axially aligned shaft accommodating openings, one ofsaid housing wall's being provided with means to'store by gravity a volume of 1 said liquid seal when the shaftportion and impeller are-stationary, including the surface'of a liquid seal reservoir, merging into =the surface of said chamber, saidentire reservoir surface being wholly below a horizontal-plane through said shaft portion'and extending" upwardly 'to' said shaft portion.

' FRANK-H;- FLETCHER, JR.

CITED The following references are of record inthe file of. this patent;

U l- D- ST T- s T NT 

